Conventional utility blades are made of carbon steel and define a back edge, a cutting edge located on an opposite side of the blade relative to the back edge, and two side edges located on opposite sides of the blade relative to each other and extending between the back and cutting edges of the blade. A pair of notches are typically formed in the back edge of the blade for engaging a locator in a blade holder. Typically, the back, cutting and side edges of the blade define an approximately trapezoidal peripheral configuration. However, prior art utility blades have been commercially available for many years in a variety of shapes other than trapezoidal, such as rectangular or hooked blades. In addition, prior art utility blades have been provided in snap-off configurations wherein a single blade includes axially spaced score lines and separable blades or blade segments therebetween.
Conventional utility blades are manufactured by providing a carbon steel strip, running the strip through a punch press to punch the notches at axially spaced locations on the strip, and stamping a brand name, logo or other identification thereon. Then, the strip is scored to form a plurality of axially spaced score lines, wherein each score line corresponds to a side edge of a respective blade and defines a preferred breaking line for later snapping the scored strip into a plurality of blades. The punched and scored strip is then wound again into a coil, and the coil is hardened and tempered. The hardening and tempering operations may be performed in a “pit-type” vacuum furnace wherein the coils are repeatedly heated and cooled therein. Alternatively, the hardening and tempering operations may be performed “in-line”, wherein the strip is unwound from the coil and successively driven through a series of furnaces and quenching stations to harden and temper the strip. The carbon steel strip is typically heat treated to a surface hardness of about 58 Rockwell “c” (“Rc”), and thus defines a relatively hard and brittle structure.
The heat treated strip is then ground, honed and stropped in a conventional manner to form the facets defining a straight cutting edge along one side of the strip. Then, the strip is snapped at each score line to, in turn, break the strip along the score lines and thereby form from the strip a plurality of trapezoidal or other shaped utility blades. Because the entire strip is relatively hard and brittle (about 58 Rc), the strip readily breaks at each score line to thereby form clean edges at the side of each blade.
One of the drawbacks associated with such conventional utility blades is that each blade is formed of a single material, typically carbon steel, which is heat treated to a relatively hard and brittle state, typically about 58 Rc. Thus, although such blades define a relatively hard, wear-resistant cutting edge, the entire blade is also relatively brittle, and therefore is subject to premature breaking or cracking in use. In addition, the cutting edges of such conventional blades are frequently not as wear resistant as might otherwise be desired. However, because the entire blade is made of the same material, any increase in hardness, and thus wear resistance of the cutting edge, would render the blade too brittle for practical use. As a result, such conventional utility blades are incapable of achieving both the desired wear resistance at the cutting edge, and overall toughness to prevent cracking or premature breakage during use. Another drawback of such conventional utility blades is that the carbon steel typically used to make such blades corrodes relatively easily, thus requiring premature disposal of the blades and/or costly coatings to prevent such premature corrosion.
Certain prior art patents teach composite utility blades defining sandwiched, laminated, or coated constructions. For example, U.S. Pat. No. 4,896,424 to Walker shows a utility knife having a composite cutting blade formed by a body section 16 made of titanium, and a cutting edge section 18 made of high carbon stainless steel and connected to the body section by a dovetail joint 25.
U.S. Pat. Nos. 3,279,283, 2,093,874, 3,681,846, and 6,105,261 relate generally to laminated knives or razor blades having cutting edges formed by a core layer made of a high carbon steel or other relatively hard material, and one or more outer layers made of relatively softer materials. Similarly, U.S. Pat. Nos. 3,911,579, 5,142,785, and 5,940,975 relate to knives or razor blades formed by applying a relatively hard carbon coating (or diamond like coating (“DLC”)) to a steel substrate. In addition, U.S. Pat. Nos. 5,317,938 and 5,842,387 relate to knives or razor blades made by etching a silicon substrate.
One of the drawbacks associated with these laminated, sandwiched and/or coated constructions, is that they are relatively expensive to manufacture, and therefore have not achieved widespread commercial use or acceptance in the utility blade field.
In stark contrast to the utility blade field, bi-metal band saw blades have been used in the saw industry for many years. For example, U.S. Reissue Pat. No. 26,676 shows a method of making bi-metal band saw blades wherein a steel backing strip and high speed steel wire are pre-treated by grinding and degreasing, and the wire is welded to the backing strip by electron beam welding. Then, the composite band stock is straightened and annealed. The sides of the annealed stock are then dressed, and the band saw blade teeth are formed in the high speed steel edge of the composite stock by milling. Then, the teeth are set and the resulting saw blade is heat treated. There are numerous methods known in the prior art for heat treating such band saw blades. For example, International Published Patent Application No. WO 98/38346 shows an apparatus and method for in-line hardening and tempering composite band saw blades wherein the blades are passed around rollers and driven repeatedly through the same tempering furnace and quenching zones. The heat treated composite band saw blades are then cleaned and packaged.
Although such bi-metal band saw blades have achieved widespread commercial use and acceptance over the past 30 years in the band saw blade industry, there is not believed to be any teaching or use in the prior art to manufacture utility blades defining a bi-metal or other composite construction as with bimetal band saw blades. In addition, there are numerous obstacles preventing the application of such band saw blade technology to the manufacture of utility blades. For example, as described above, conventional utility blades are manufactured by forming score lines on the carbon steel strip, and then snapping the strip along the score lines to break the strip into the trapezoidal or other shaped blades. However, the relatively tough, spring-like backing used, for example, to manufacture bi-metal band saw blades, can be relatively difficult to score and snap in comparison to conventional carbon steel utility blades. In addition, the heat treating applied to conventional utility blades could not be used to heat treat bimetal or other composite utility blades.
The high speed or tool steels used to manufacture wear-resistant cutting edges, such as the wear-resistant cutting edges in prior art band saw blades, are relatively expensive in comparison, for example, to the carbon steels used to manufacture conventional utility blades. In addition, the grinding and honing operations involved in forming wear-resistant cutting edges from high speed and tool steels can create significant amounts of scrap and/or waste of these expensive materials.
Accordingly, it is an object of the present invention to overcome one or more of the above-described drawbacks and disadvantages of prior art utility blades and/or methods of making such blades, and to provide a bi-metal or other composite utility blade defining a relatively hard, wear-resistant cutting edge, and a relatively tough, spring-like backing, and a method of making such utility blades.